This invention relates to digital computer network technology. More specifically, the present invention relates a new fiber node configuration to be implemented in cable networks.
Broadband access technologies such as cable, fiber optic, and wireless have made rapid progress in recent years. Recently there has been a convergence of voice and data networks which is due in part to US deregulation of the telecommunications industry. In order to stay competitive, companies offering broadband access technologies need to support voice, video, and other high-bandwidth applications over their local access networks. For networks that use a shared access medium to communicate between subscribers and the service provider (e.g., cable networks, wireless networks, etc.), providing reliable high-quality voice/video communication over such networks is not an easy task.
One type of broadband access technology relates to cable modem networks. A cable modem network or “cable plant” employs cable modems, which are an improvement of conventional PC data modems and provide high speed connectivity. Cable modems are therefore instrumental in transforming the cable system into a full service provider of video, voice and data telecommunications services. Digital data on upstream and downstream channels of the cable network is carried over radio frequency (“RF”) carrier signals. Cable modems convert digital data to a modulated RF signal for upstream transmission and convert downstream RF signal to digital form. The conversion is done at a subscriber's facility. At a Cable Modem Termination System (“CMTS”), located at a Head End of the cable network, the conversions are reversed. The CMTS converts downstream digital data to a modulated RF signal, which is carried over the fiber and coaxial lines to the subscriber premises. The cable modem then demodulates the RF signal and feeds the digital data to a computer. On the return path, the digital data is fed to the cable modem (from an associated PC for example), which converts it to a modulated RF signal. Once the CMTS receives the upstream RF signal, it demodulates it and transmits the digital data to an external source.
FIG. 1 shows a block diagram of a conventional cable network 100. The cable network 100 includes a Head End 102 which provides a communication interface between nodes (e.g. cable modems) in the cable network and external networks such as, for example, the Internet. The cable modems typically reside at the subscriber premises 110a–d. 
The Head End 102 is typically connected to one or more hubs 104. Each hub is configured to service one or more fiber nodes 106 in the cable network. Each fiber node is, in turn, configured to service one or more subscriber groups 110. Each subscriber group typically comprises about 500 to 2000 households. A primary function of the fiber nodes 106 is to provide an optical-electronic signal interface between the Head End 102 and the plurality of cable modems residing at the plurality of subscriber groups 110.
Communication between the Head End 102, hub 104, and fiber node 106a is typically implemented using modulated optical signals which travel over fiber optic cables. More specifically, during the transmission of modulated optical signals, multiple optical frequencies are modulated with data and transmitted over optical fibers such as, for example, optical fiber links 103 and 105a,b of FIG. 1, which are typically referred to as “RF fibers”.
As shown in FIG. 1, the modulated optical signals transmitted from the Head End 102 eventually terminate at the fiber node 106a. The fiber nodes maintain the RF modulation while converting from the fiber media to the coax media and back.
FIG. 2 shows a block diagram of a conventional fiber node 200 such as, for example, fiber node 106a of FIG. 1. In conventional cable networks, the fiber node 200 is responsible for converting RF modulated wavelength optical signals into electrical signals and vice versa. The RF modulated optical signals enter the fiber node 200 via downstream RF fiber 205, and are converted into electric signals by the optical-to-electric signal converter 202. The electrical signals are then amplified by downstream amplifier 204. The amplified electric signals are then passed to a diplexor 210 which transmits the electric signals over the coaxial line 209 to the plurality of cable modems.
In the reverse direction, the cable modems transmit electrical signals via the coaxial line 209 to the fiber node 200. The upstream electrical signals from the cable modems are received at the diplexor 210, and passed to the upstream amplifier 206. The upstream electrical signals are then passed from the amplifier 206 to an electric-to-optical signal converter, which converts the upstream electric signals into radio frequency wavelength modulated optical signals which are then transmitted to the Head End via upstream RF fiber 207.
Typically, the use of RF modulated optical signals in the cable network 100 only allows for very narrow opportunities to transmit IP packets. This is because most of the bandwidth of the RF modulated optical signal is used for DOCSIS related signaling between the Head End 102 and plurality of cable modems.
As a result, most conventional cable networks are not equipped to handle increased data flows relating to new and emerging broadband network applications such as video-on-demand, telephony, etc. Accordingly, there exists a continual need to improve access network configurations in order to accommodate new and emerging network applications and technologies.